Four intact female monkeys received two capsules of Norplant~ containing 70 mg each of levonorgestrel (LNG) placed subdermally in the interscapular region. All animals had one pre-treatment blood sample drawn prior to capsule insertion, daily on days 1 through 7, then once per week for 14 months. The animals' menstrual calendars have been evaluated throughout the study for amenorrhea, intermenstrual bleeding and the duration and intensity of the bleeding. The animals were observed for any local reactions at the capsule insertion site and palpated once per month for the presence of the two capsules. Serum analyzed for lng showed levels dropping rapidly from 14.1 Ng/ml (sem 2.4) On day 1 to 3.0 Ng/ml (sem 0.3) On day 28 then gradually dropping to 1.8 Ng/ml (sem 0.1) On day 427 of the study. LNG levels have remained fairly constant out to study day 840. The capsules have been palpable for all animals out to day 413 of the study. No local reactions were noted. The animals' menstrual calendars have shown amenorrhea for two of the four animals and irregular but light menstrual bleeding for the remaining two animals. Collection of serum will continue until levels of LNG fall below level of contraceptive effectiveness which is 0.3 Ng/ml. Menstrual calendar observations will continue for the duration of the study.